The Fixes commit mentioned this:
> An MPTCP firewall blackhole can be detected if the following SYN
> retransmission after a fallback to "plain" TCP is accepted.
But in fact, this blackhole was detected if any following SYN
retransmissions after a fallback to TCP was accepted.
That's because 'mptcp_subflow_early_fallback()' will set 'request_mptcp'
to 0, and 'mpc_drop' will never be reset to 0 after.
This is an issue, because some not so unusual situations might cause the
kernel to detect a false-positive blackhole, e.g. a client trying to
connect to a server while the network is not ready yet, causing a few
SYN retransmissions, before reaching the end server.
Fixes: 27069e7cb3d1 ("mptcp: disable active MPTCP in case of blackhole")
Cc: stable@xxxxxxxxxxxxxxx
Reviewed-by: Mat Martineau <martineau@xxxxxxxxxx>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@xxxxxxxxxx>
---
net/mptcp/ctrl.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/net/mptcp/ctrl.c b/net/mptcp/ctrl.c
index 3999e0ba2c35b50c36ce32277e0b8bfb24197946..2dd81e6c26bdb5220abed68e26d70d2dc3ab14fb 100644
--- a/net/mptcp/ctrl.c
+++ b/net/mptcp/ctrl.c
@@ -418,9 +418,9 @@ void mptcp_active_detect_blackhole(struct sock *ssk, bool expired)
MPTCP_INC_STATS(net, MPTCP_MIB_MPCAPABLEACTIVEDROP);
subflow->mpc_drop = 1;
mptcp_subflow_early_fallback(mptcp_sk(subflow->conn), subflow);
- } else {
- subflow->mpc_drop = 0;
}
+ } else if (ssk->sk_state == TCP_SYN_SENT) {
+ subflow->mpc_drop = 0;
}
}
--
2.47.1
